This Specialized Aethos fixed-gear conversion is the coolest bike we’ve seen this year

Meet the 'Randonnaethos'

Erik Nohlin's fixed-gear Specialized Aethos 'Randonnaethos'

What happens when you leave a Specialized Aethos in the hands of the brand’s fixie-fanatic designer, Erik Nohlin?


Well, this is what – a fascinating fixed-gear conversion designed and custom-specced for long-distance randonneur rides, replete with disc brakes, dynamo lighting, a rack and 3D-printed saddle, all based around a 585g S-Works Aethos frame.

It’s a bike that speaks wholly to Nohlin’s love of fixed-gear riding – “no other form of cycling gets me into that deep state of meditation,” he says – and also pays tribute to his friend, Metin Uz, who died in May.

“When trying to make sense of this tragedy, I realised that the best thing I could do was to continue Metin’s fixed-gear legacy and build up my new randonneuring bike in his memory,” Nohlin told BikeRadar.

The bike – dubbed the ‘Randonnaethos’ by Nohlin – is made possible, in part, by an eccentric bottom bracket and a smattering of home workshop hacks.

That included drilling the seatpost (warning: this will void your warranty!) to route the dynamo wiring – “it snakes through the post, seat tube, down tube and down the fork” – and adapting the Aethos’s existing derailleur hanger.

“I machined the derailleur hanger to use only the upper part that indexes the hub in the dropout,” Nohlin wrote in an Instagram post (@hellhommus) documenting the build. “When the standard thru-axle slides out of the [hub], the wheel pops right out by gravity. This enables a very fast flat fix with no need to tension the chain or re-position the wheel straight in the frame.”

We caught up with Nohlin, a lead designer at Specialized, to find out more about this remarkable bike – a machine he calls an “eclectic mix between LoFi and HiFi”.

First up, why did you put this build together?

Erik Nohlin’s build started with a 56cm Specialized S-Works Aethos RFP frame.
Erik Nohlin

It might seem like a stupid thing to do, building a fixed-gear bike out of an Aethos, especially living in the hilliest cities in the United States – but to me, it makes total sense. In fact, I felt that I had to.

In the spring of 2022, as the Super-Randonneur season with San Francisco Randonneurs wrapped up, I got to ride the 600km Mendocino Coast alongside fixed-gear randonneur Metin Uz, a longtime member of our club that I’ve ridden countless brevets with over the years.

Nohlin’s ‘Randonnaethos’ came together through careful adaptation of the Aethos frame and considered component selections.
Erik Nohlin

We rode most of the brevet together. Just two weeks later, during the Treasure Cove 1200 in Virginia, Metin was struck and killed, about 220 miles into the ride.

When trying to make sense of this tragedy, I realised that the best thing I could do was to continue Metin’s fixed-gear legacy and build up my new randonneuring bike in his memory.

What was your inspiration for the build?

Specialized launched the Aethos in 2019 as a round-tubed antidote to the aero-inspired bikes common at the top-end of the market.

This is a story in itself. I once had another Aethos – for a day. It was the flagship in my bike collection – a totally ridiculous bike that I painted and built myself for the 2019 Chris King Open House exhibition.

It was based on the Aethos Founder’s Edition [limited to 300 bikes at launch and the lightest Specialized Aethos build on offer at 5.9kg– ed] and had everything customised and curated to be my “forever bike”.

Well, on the morning of the launch, I spoke to a member of the bicycle press calling it just that. I jinxed it. A few hours later, on the maiden voyage, I was struck by a reckless driver making an illegal U-turn and the ultra-light bike exploded underneath me as we T-boned a Honda Civic at almost 50km/h.

I got so messed up that it kept me off bikes for a full year and, once ready to even consider building a new bike, the global supply chain issues that we all felt prevented me from getting a replacement frame for almost another full year.

Me getting back onto bikes after a long stint of psychotherapy coincided with Metin’s death and I decided that it was now or never. Either I fought to re-establish my love for the distance, or I was just going to leave it there.

The fine people at Specialized Retail Care were able to find me a frame and, during the autumn, I’ve slowly been collecting parts to build another ridiculous, but very different Aethos.

Can you talk us through the key component choices?

The RFP (Ready for Paint) frame sees a satin clear coat laid over the raw carbon frame.
Erik Nohlin

The frameset is the S-Works RFP (Ready for Paint) in a size 56. This means satin-cleared raw carbon with the decals on the outside to allow for custom paint.

As this is a bike built for the ultra-distance, a dynamo setup was a must, and I already had a Son hub and a Supernova light setup from before. The 28-hole hub would make for some very strong wheels. Not the lightest, but very strong.

I opted for some low-profile H Plus Son [TB14] rims to achieve some classic elegance. The dynamo is internally routed. The rear hub is the legendary WORD fixed-gear hub from my friends at Paul Components, also 28h [the Wacky One-Speed Rear Device – WORD – was the first purpose-built singlespeed mountain bike hub when it was released in 1996 – ed].

This classic hub, then the first of its kind, is a very high-quality hub that allows me to run disc brakes, a must for me.

A dynamo-equipped Aethos? You bet! This is a SONdelux hub.
Erik Nohlin

The randonneuring bag is from the collection I designed as a collaboration between Specialized and Swedish brand Fjällräven, which consists of a stand-alone rack with a light mount, and an 8-litre bag that fits everything I need for even the longest rides.

The saddle is the 3D-printed Specialized Romin Evo and the cranks might be the most special part of them all. In 2012, I rode the first Transcontinental Race from London to Istanbul with these cranks on my belt-driven AWOL.

A nod to the future of bike components with this 3D-printed Specialized Romin Evo saddle.
Erik Nohlin

Not at all fancy or light, but we’ve been through heaven and hell together, so I figured we’ll just continue that theme on this new bike.

Finally, what enables me to set up a stock Aethos fixed gear, is the eccentric bottom bracket from Phil Wood.

28-hole hubs front and rear make for very strong wheels.
Erik Nohlin

What gear are you running?

This Phil Wood Philcentric bottom bracket makes the fixed-gear conversion possible. The outboard bottom bracket allows for “eccentricity without using horizontal dropouts, an eccentric hub or chain tensioners”, according to Phil Wood, a component manufacturer based in San Jose, California.
Erik Nohlin

The eccentric bottom bracket enables me to ride one heavier gear than the 46×18 I currently have on, without making the chain shorter.

46×18 is a total compromise for me. I’m usually a strong rider on a heavy gear, riding fast, but our local routes always include a few climbs, which now force me to pick a lighter gear.

Nohlin runs a 46x18t gear.
Erik Nohlin

This also forces me to ride slower and spin more than I’m used to but hey, that’s the beauty with fixed-gear randonneuring. It’s you and the bike, and the environment dictates your speed.

That’s what I love about fixed-gear riding, the direct drive and connection to the tarmac. No other form of cycling gets me into that deep state of meditation.

What’s it like running disc brakes on a fixie?

TRP Hylex brakes provide the stopping power. “I did a full brevet season on a brakeless fixed-gear bike and I’ll never do that again,” Nohlin says.
Erik Nohlin

It’s a must for me these days. Especially when riding with others.

In 2009, I did a full brevet season on a brakeless fixed-gear bike and I’ll never do that again – some fun but stupid shit!

The Hylex is a singlespeed-specific disc brake system.
Erik Nohlin

The TRP Hylex brakes enable me to ride safely and it significantly reduces stress on my knees going downhill and braking.

At 44, my knees are more sensitive to stress than they used to be and the disc brakes enable me to relax and focus on riding in a way that brakeless doesn’t.

TRP calipers – not that you’d know it.
Erik Nohlin

What’s the final weight of the bike?

6.66kg, of course.

If you follow me on social (@hellhommus) you know that my Black Metal addiction and fascination for the dark arts, forces me to say that…

In reality, I’m not sure. The bike is not built to be a weight weenie. I bet I could have gotten it below 5kg, but with the dynamo lights, rack and crank setup, I bet it’s closer to 7kg. Funny how the front hub and disc weighs the same as the frame (585g).

What I wanted to achieve here was a bike that is incredibly comfortable for the distance, while also being trustworthy.

My previous Aethos was one of the most comfortable bikes I had ever ridden and when you find a bike that fits you that well, that’s a great start for making it even better through smart component selections.

What riding are you planning for the bike?

Well, there are so many rides I haven’t done.

First, I guess getting [the Aethos] out on our friend Metin’s old roads in Marin and Mendocino counties, but then who knows.

Expect Nohlin’s 28mm Specialized Turbo Pro T5 tyres to see plenty of miles next year.
Erik Nohlin

I hope there will be more PBPs [Paris-Brest-Paris, the 1,200km long-distance event from the French capital to the Brittany coast and back] and 1,200km brevets in the future, but I’m humble about my own vulnerability, so focusing on one ride at a time makes sense.

There’s one remaining brevet with San Francisco Randonneurs in December and I hope I will be able to premiere the bike there.

A Supernova E3 Triple 2 dynamo light provides always-on illumination.
Erik Nohlin

Is there anything else you want to tell us about the bike?

Nohlin drilled the Roval Alpinist seatpost to provide internal cable routing for the Supernova E3 2 rear light.
Erik Nohlin

Well, as an employee of Specialized, I should mention that drilling any parts is not recommended.

Not only will it void the warranty, but it can also be dangerous.

The dynamo wiring “snakes through the post, seat tube, down tube and down the fork”.
Erik Nohlin

As a professional, I did make some carbon customisations to internally wire the dynamo lights, but I wouldn’t recommend it.

I hope some of you get inspired by this build. I know hill climbing is quite big in the UK and something I’ve been active in myself. This bike could become even more ridiculous in a hill-climbing build.

In general, I dare you all to help keep the fixed-gear format alive. It’s an incredibly pure and timeless type of cycling.

And finally, are you happy with the end product?

“I love the eclectic mix between LoFi and HiFi in this build,” Nohlin says. “The world’s lightest production frame and a dynamo hub… That friction is great!”
Erik Nohlin

Yeah, really excited. It rides like a dream. An incredible bike.

It’s cool that small independent component makers like Paul and Phil still care about the fringe cultures of cycling and weirdos like me. They play a vital role in making cycling richer in expression.

Titanium cages and Maurten bottles finish the build.
Erik Nohlin

I love the eclectic mix between LoFi and HiFi in this build. The world’s lightest production frame and a dynamo hub… That friction is great!

I’m not much for naming my bikes but Randonnaethos became a hashtag when posting about the process and you can find some more details on Instagram under it.

Erik Nohlin’s ‘Randonnaethos’ – full specification

Erik Nohlin’s fixed-gear Specialized Aethos ‘Randonnaethos’.
Erik Nohlin
  • Frameset: Specialized S-Works Aethos RFP, size 56cm
  • Brakes: TRP Hylex hydraulic disc
  • Bottom bracket: Phil Wood Philcentric
  • Crankset: SRAM Rival, 46t
  • Sprocket: Mash SF, 18t
  • Handlebar: Specialized Hover Alloy Handlebar – 15mm Rise plus Flare
  • Stem: Specialized S-Works SL 80mm
  • Seatpost: Roval Terra Carbon
  • Hubs: SONdelux dynamo 28h (front), Paul Components WORD 28h (rear)
  • Rims: H Plus Son TB14
  • Tyres: Specialized Turbo Pro T5, 28mm
  • Inner tubes: Pirelli P-Zero SmarTUBE
  • Pedals: Shimano SPD-SL
  • Rack: Specialized x Fjällräven Exchange Handlebar Rack
  • Bag: Specialized x Fjällräven Exchange Handlebar Bag
  • Bottle cages: Specialized Ti
  • Bottles: Maurten
  • Lights: Supernova E3 Triple 2 (front), Supernova E3 2 (rear)